linux-kernel - Re: [PATCH 4/5] ceph: fix improper use of smp_mb__before

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Date:   Thu, 9 May 2019 22:55:43 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     "Yan, Zheng" <ukernel@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Yan, Zheng" <zyan@...hat.com>, Sage Weil <sage@...hat.com>,
        Ilya Dryomov <idryomov@...il.com>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 4/5] ceph: fix improper use of smp_mb__before_atomic()

On Tue, Apr 30, 2019 at 05:08:43PM +0800, Yan, Zheng wrote:
> On Tue, Apr 30, 2019 at 4:26 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Mon, Apr 29, 2019 at 10:15:00PM +0200, Andrea Parri wrote:
> > > This barrier only applies to the read-modify-write operations; in
> > > particular, it does not apply to the atomic64_set() primitive.
> > >
> > > Replace the barrier with an smp_mb().
> > >
> >
> > > @@ -541,7 +541,7 @@ static inline void __ceph_dir_set_complete(struct ceph_inode_info *ci,
> > >                                          long long release_count,
> > >                                          long long ordered_count)
> > >  {
> > > -     smp_mb__before_atomic();
> >
> > same
> >         /*
> >          * XXX: the comment that explain this barrier goes here.
> >          */
> >
> 
> makes sure operations that setup readdir cache (update page cache and
> i_size) are strongly ordered with following atomic64_set.

Thanks for the suggestion, Yan.

To be clear: would you like me to integrate your comment and resend?
any other suggestions?

Thanx,
  Andrea


> 
> > > +     smp_mb();
> >
> > >       atomic64_set(&ci->i_complete_seq[0], release_count);
> > >       atomic64_set(&ci->i_complete_seq[1], ordered_count);
> > >  }
> > > --
> > > 2.7.4
> > >